Conventionally, a plurality of switches on a route carried out the determination of a route for a packet from a transmission source to a transmission destination, and packet transfer processing. In recent years, in a large scale network such as a data center, the change of a network configuration often occurs because of the new addition of equipment for a scale expansion and the stop of equipment due to a failure. Therefore, the flexibility to cope with the change of the network configuration and to determine an appropriate route became necessary. However, because a program for route determination processing in the switch cannot be changed externally, the whole network cannot be controlled and managed in an integrated manner.
On the other hand, in a computer network system, an (open flow) technique of controlling a transfer operation of each of all the switches by an external controller is proposed by Open Networking Foundation (Non-Patent Literature 1). The network switch corresponding to this technique (hereinafter, to be referred to as open flow switch (OFS)) holds detailed data such as a protocol type and a port number in a flow table and can carry out the control of a flow and the collection of statistical data.
In a system using an open flow protocol, setting of a communication route and setting for a transfer operation (relay operation) to the switches OFS on the route are carried out by an open flow controller (hereinafter, to be referred to as OFC). OFC is also to be referred to as a programmable flow controller. At this time, the controller OFC sets in a flow table of the switch, a flow entry which a rule for specifying a flow (packet data) and an action for defining an operation to the flow are related to each other. The switch OFS on the communication route determines a destination of reception packet data according to the flow entry set by the controller OFC and carries out transfer processing of the packet data. Thus, a client terminal becomes possible to transmit and receive packet data to and from another client terminal by using the communication route set by the controller OFC. That is, in the computer system using an open flow technique, the controller OFC for setting the communication route and the switches OFS for carrying out the transfer processing are separated, and the communication of the whole system can be controlled and managed in an integrated manner.
Because the controller OFC can control the transfer between the client terminals in units of flows based on the header data of L1 to L4, the controller OFC can virtualize the network optionally. Thus, because the constraints of a physical configuration can be eased, the building of virtual tenant environment becomes easy, so that it is possible to reduce an initial investment cost by scale out.
When the number of terminals such as client terminals, servers, and storages to be connected with the system using the open flow technique increases, the load of the controller OFC which manages the flow increases. Therefore, in order to reduce the load of the controller OFC, there is a case where a plurality of controllers OFC are installed in one (network) system. Or, generally, because one controller OFC is provided for every data center, a plurality of the controllers OFC manage the network in the whole system in case of the system which has a plurality of data centers.
The system in which one network is managed by the plurality of controllers is disclosed in, for example, JP 2011-166692A (Patent Literature 1), JP 2011-166384A (Patent Literature 2), and JP 2011-160363A (Patent Literature 3). Patent Literature 1 discloses a system in which a plurality of controllers sharing topology data carries out the flow control of the network using the open flow technique. Patent Literature 2 discloses a system which includes a plurality of controllers which instruct the setting of a flow entry with a priority to switches on a communication route, and the switches which determine permission/non-permission of the setting of the flow entry according to the priority, and carry out a relay operation to a reception packet conforming with the flow entry set to itself. Patent Literature 3 discloses a system which includes a plurality of controllers which instruct the setting of a flow entry to switches on a communication route, and the switches which carry out a relay operation to a reception packet according to the flow entry set by a route determining controller as one of the plurality of controllers.